1. Field of the Invention
The present invention relates to a wiring board.
2. Description of the Related Art
Conventionally, a technique is known to provide a high density wiring layer in a wiring board with a built-in passive component. Specifically, a wiring board is known in which a high wiring density layer including stacked insulating layers of photosensitive resin is formed on a low wiring density layer including stacked insulating layers of thermosetting resin. In such a case, a passive component is built-in the low wiring density layer.
It is described that the wiring layer can be made high density by embedding a wiring layer at a surface of a core board in an insulating layer (thermosetting resin) at the surface of the core board, in the low wiring density layer, and forming the high wiring density layer on the low wiring density layer in the above described wiring layer (see Patent Document 1, for example).
However, as the above described wiring board has an asymmetry structure in an up and down direction, there is a problem in that a warp is generated in the wiring board. The warp generated in the wiring board may be a problem when mounting an electronic component on the high wiring density layer.
Further, according to the above method described in Patent Document 1, a fine wiring cannot be formed in the insulating layer (thermosetting resin) at the surface of the core board and the fine wiring needs to be formed on an insulating layer of photosensitive resin formed on the insulating layer (thermosetting resin) at the core board.
In other words, as the fine wiring cannot be directly formed in the insulating layer (thermosetting resin) just by embedding the wiring layer at the surface of the core board in the insulating layer (thermosetting resin), the wiring layer cannot be made at a sufficiently high density.